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Ultraviolet Spectra of QSOs, BL Lacertae Objects, and Seyfert Galaxies
Turnshek, David A.; Lanzetta, Kenneth M.; Sandoval, Jennifer
Motivated by the possibility of detecting strong absorption features toward extragalactic background objects, we present optimally extracted and co-added IUE spectra of QSOs, BL Lac objects, and Seyfert galaxies. These spectra together with those presented (in a similar work) by Kinney et al. form an essentially complete sample of the SWP, LWP, an…
The extended formaldehyde source in comet P/Halley
Eberhardt, P.; Meier, R.; Krankowsky, D. +1 more
The Neutral Mass Spectrometer on the Giotto spacecraft measured the neutral and ion composition in the coma of comet P/Halley. In the ion mass spectra, the 31 amu/e peak is dominated by the protonated formaldehyde ion H3CO+ and can be used to calculate the H2CO density. The radial profile of the amplitude of the 31…
ROSAT studies of the composition and structure of DA white dwarf atmospheres.
Barstow, M. A.; Koester, D.; Sansom, A. E. +7 more
We present here a detailed study of a sample of hot I)A white dwarfs detected in the EUV and soft X-ray bands by ROSAT during its all-sky survey. The survey data are combined with additional ROSAT pointed-phase observations, earlier EXOSAT results and the available optically determined effective temperatures and gravities. We show that the spectra…
Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304. I. The IUE Campaign
Maraschi, L.; Chiappetti, L.; Tagliaferri, G. +26 more
Daily monitoring of PKS 2155 - 304 with the IUE satellite throughout 1991 November has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux of this BL Lac object. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5^d^ period when sampling was roughly continuous, the rapid flaring h…
The Hubble Space Telescope Snapshot Survey. IV. A Summary of the Search for Gravitationally Lensed Quasars
Gould, A.; Maoz, D.; Meylan, G. +7 more
We report the concluding results of the HST Snapshot Survey for gravitationally lensed quasars. New observations of 153 high-luminosity z > 1 quasars are presented, bringing to 498 the total number of quasars observed in the survey. The new observations do not reveal new candidates for gravitational lensing. We present tables summarizing all of…
Further probing of the X-ray source in NGC 4151 : new constraints on the nuclear geometry.
Sokoloski, J. L.; Yamauchi, M.; Warwick, R. S. +4 more
We report on the results of new Ginga observations of the archetypal Seyfert galaxy, NGC 4151, performed over an 18-month period between early 1990 and mid-1991. The present programme complements earlier extensive monitoring of this source in the medium-energy X-ray band by both EXOSAT and Ginga to give a combined data set of some 36 separate obse…
X-Ray Observations of the Warm Absorber in NGC 3783
Nandra, K.; Turner, T. J.; Fabian, A. C. +2 more
We present a high signal-to-noise ROSAT position sensitive proportional counter (PSPC) observation of the Seyfert 1 galaxy NGC 3783. The 0.1-2.5 keV spectrum shows strong evidence for an absorption edge most likely associated with O VII-VIII. Such a feature, which has now been detected in a number of PSPC spectra (Nandra et al.; Nandra & Pound…
Observational Constraints on the Lifetime of Cometary H 2O
Cochran, Anita L.; Schleicher, David G.
We used a carefully selected set of observations of five comets along with a vectorial model and the Haser model to explore the lifetimes against photodissociation of H2O and OH in cometary comae. The photometric and long-slit CCD data described in this paper were obtained specifically for this project, while the IUE data are archival. …
The Crab Pulsar in the Visible and Ultraviolet with 10 Microsecond Time Resolution
Dolan, J. F.; Nelson, M. J.; Percival, J. W. +8 more
Observations of PSR 0531+21 with the High Speed Photometer on the HST in the visible in October 1991 and in the UV in January 1992 are presented. The time resolution of the instrument was 10.74 microsec; the effective time resolution of the light curves folded modulo the pulsar period was 21.5 microsec. The main pulse arrival time is the same in t…
A Determination of the Distance to the High-Velocity Cloud Complex M
Kuntz, K. D.; Danly, Laura; Albert, C. E.